The present invention relates generally to a valve timing control (VTC) apparatus for controlling valve timings of an internal combustion engine such as opening and closing timings of engine valves such as intake and exhaust valves, and more particularly to a valve timing control apparatus which actuates a phase alteration mechanism with an alternating torque of a camshaft and a hydraulic pressure.
A Japanese Patent Application Publication No. 2005-147153 (henceforth referred to as “JP2005-147153”) shows a camshaft phasing device or valve timing control apparatus of a vane type, which employs: a cam torque actuated (CTA) phaser or camshaft-torque actuation mechanism to rotate a vane member with fluctuations of an alternating torque of a camshaft as a driving source; and an oil pressure actuated (OPA) phaser or hydraulic actuation mechanism to rotate the vane member with a discharge pressure of an oil pump as a driving source.
Specifically, in the conventional valve timing control apparatus, a cylindrical housing is closed at its front open end by a front cover and is closed at its rear open end by a rear cover. A vane member including a plurality of CTA vanes and a plurality of OPA vanes is rotatably disposed within the housing. The CTA vanes are driven in one rotational direction by fluctuations of the alternating torque of a camshaft, whereas the OPA vanes are driven in the opposite rotational direction by the discharge pressure of the oil pump. The vane member is coupled at its central portion to an end of a camshaft, such as an exhaust camshaft.
The housing is formed with a plurality of shoes in the inside peripheral surface. Each of the vanes of the vane member and the shoes of the housing define an advance fluid pressure chamber and a retard fluid pressure chamber. A solenoid-type control valve is disposed slidably within the vane member to supply and drain an oil pressurized by the oil pump to and from the fluid pressure chambers.
The CTA vanes are rotated in one rotational direction by the camshaft-torque actuation mechanism including the control valve when the discharge pressure of the oil pump is low, for example, at the time of engine start or at the time of low speed engine operation, whereas the OPA vanes are rotated in the opposite rotational direction by the hydraulic actuation mechanism when the discharge pressure of the oil pump is high, for example, at the time of high speed engine operation.
The vane member is rotated in normal and reverse directions by the alternating torque and the hydraulic pressure, resulting in an alteration in the valve timing phase or the relative rotational phase of the camshaft with respect to a timing pulley. Thus, the opening and closing timings of each exhaust valve is controlled in accordance with the engine operating conditions.